The purpose of the project is to determine early morphological and histochemical changes leading to cataract in mammalian lenses. Clincal, light microscopic and electron microscopic approaches are being employed. The histochemical experiments includes analyses for acid phosphatase and other lysosomal hydrolases, as well as enzymes linked to sodium and potassium transport. The enzymes being localized are those which have been biochemically demonstrated by others in the lens. The sources of cataractous lenses used in the project include: (a) Wistar rats of a strain commonly developing senile cataract; (b) Wistar rats with X-ray-induced cataract mutation; and (c) gamm-irradiated rabbit eyes. In addition, aged human lenses are being observed clinically at yearly intervals, and microscopically after cataract surgery.